This invention relates to an image processing apparatus and method for performing saturation conversion.
In general, an image processing apparatus for forming a multi-valued image performs so-called saturation conversion to obtain an image with appropriate saturation by compensating saturation for a less saturated area in an image, and suppressing saturation for an oversaturated area.
In order to implement saturation conversion in a conventional image processing apparatus, saturation values (normally ranging from 0.0 to 1.0) are calculated in units of pixels in an image, and the saturation value of each pixel is corrected by multiplying the saturation value by a predetermined saturation conversion parameter.
However, the conventional image processing apparatus always performs saturation conversion based on a saturation conversion parameter with a constant value regardless of the image feature of the image to be converted.
In general, of colors that the image processing apparatus can reproduce, the flesh tone of a human being, green of plants, blue of sky, and the like are known as colors that a person especially notices and reacts sensitively to their delicate conversion results. Such colors will be referred to as “memory color” hereinafter. Optimal saturation values of these memory color vary depending on their color types. Hence, impression of an image differs depending on the saturation values of these memory color.
Hence, when a process for simply increasing or suppressing saturation at a given rate for the entire image is done regardless of the presence of memory color in the image as in the conventional apparatus, an image which can give good impression to the user cannot always be obtained. That is, it is desired to change the degree of saturation conversion in correspondence with the presence/absence of memory color in an image, or their color types if they are present.